Effective Aeration Basin Air Flow Monitoring

Municipal wastewater treatment plant uses flowmeter to effectively measure and control air flow

The aeration process requires large amounts of compressed air, and the energy cost of producing the compressed air is a big expense. The efficiency of the entire aeration process greatly depends on the management of microorganism growth, which is directly dependent on controlling the amount of air that is supplied to the basins.

Accurate airflow measurement and control of compressed air is essential to the entire wastewater treatment process—both in terms of quality results and cost control.

In the past, when selecting air flowmeters for their aeration applications, process and instrumentation, engineers often had to choose between expensive high-accuracy flow instruments and lower-cost instruments that often sacrificed accuracy or reliability.

At a typical wastewater treatment plant, each of several aeration basins is configured with several diffuser systems. The diffuser systems require individual airflow monitoring and independent control. The air flow pipes leading to the diffusers typically do not have a sufficient straight run of pipe, which makes accurate air flow measurement more difficult. Such facilities also often have a problem consistently controlling the air generated by the compressor system. The compressor system is powered 24/7, but demand changes throughout the day to accommodate various factors.

Effective measurements

The staff at a large, urban municipal wastewater treatment plant with such problems realized they needed a flowmeter that could effectively measure and control air flow over a wide flow range from 1.5 to 150 sfps, tolerate significant drops in pressure throughout the system from 0.8 to 17.6 psig, withstand temperatures from –68 to 150°F and communicate with their control system.

The treatment plant staff engineers wanted the benefits of the thermal mass flow technology with a design and price that met budgetary requirements for their aeration applications. The engineers contacted Fluid Components International (FCI), a supplier of thermal mass flowmeters used in wastewater treatment facilities, for a solution. In addition to the easy installation and lack of maintenance, the engineers wanted small size, dual analog outputs, an integral digital display of flow rate with ± 2% accuracy, ± 0.5% repeatability.

The FCI engineers responded by streamlining the feature set of their insertion-style thermal mass flowmeter and packaging it in a small but rugged enclosure with a large character, easy-to-read display that met the wastewater plant’s accuracy and repeatability specifications. After tests at the wastewater plant in which the plant engineers gave the FCI design engineers additional suggestions, the new design was finalized. The flowmeter was named the ST50, and it was approved for service.

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